The present invention relates to a plasma display panel and an imaging device using the same.
In recent years, plasma display panels (hereinafter referred to as xe2x80x9cPDPsxe2x80x9d) have attracted considerable attention as large- and flat-screen and low-profile display devices. At the present, ac-drive coplanar-discharge type PDPs (hereinafter referred to as xe2x80x9cac coplanar-discharge type PDPsxe2x80x9d) are dominant. The ac coplanar-discharge type PDP is an imaging device having a large number of small discharge spaces (discharge cells) sealed between a pair of glass substrates.
In the PDP, plasma is created by discharge of gases (discharge gases) contained in the discharge cells, and ultraviolet rays from the plasma excite phosphors to emit visible light and thereby to form an image display. There is another method of forming an image display by using a light emission directly from the plasma.
Rare gases (particularly a mixture of Ne and Xe gases) have been chiefly used as discharge gases, one of materials of the plasma display devices. Japanese Patent Application Laid-Open No. Hei 6-342631 (laid open on Dec. 13, 1994) discloses the use of a mixture of three gases He, Ne and Xe. Here, the ratio in volume of He to Ne is selected in a range of from 6/4 to 9/1, and Xe is selected in a range of from 1.5% to 10% by volume of the total of the discharge gases. However, there is a problem in that an excessive amount of He shortens lifetime of the display device. Japanese Patent Application Laid-Open No. 2000-67758 (laid open on Mar. 3, 2000) discloses a technique which controls crosstalk between adjacent discharge cells by using a mixture of three gases He, Ne and Xe and thereby increases a drive margin of a sustaining voltage. Japanese Patent Application Laid-Open No. Hei 11-103431 (laid open on Apr. 13, 1999) discloses a technique which realizes a long lifetime, stable driving voltages and proper brightness properties by using a mixture of three gases He, Ne and Xe with He and Xe being equal in concentration. It has been reported in N. Uemura, et al. xe2x80x9cKinetic Model of the VUV Production in AC-PDPs as Studied by Time-resolved Emission Spectroscopy,xe2x80x9d Proceedings of IDW ""00 (The 7th International Display Workshops), pp. 639-642 (2000)xe2x80x9d that ultraviolet ray generation efficiency is improved by using a mixture of three gases He, Ne and Xe.
Improvement in luminous efficiency (lm/W) is desired in development of PDPs. The luminous efficiency is determined by initially dividing a brightness value (or a luminance) (cd/m2) by an electric power (W/m2) required to excite a unit area to provide the above brightness value, and then correcting the obtained quotient by using a solid angle (steradian) subtended by a measurement system as viewed from the light source. Since a discharge gas has a great influence on generation of ultraviolet rays, its setting is important for the improvements of the luminous efficiency. The conditions of plasma change greatly depending upon the composition and pressure of the discharge gas, and consequently, the luminous efficiency also changes greatly. However, in the case of developing a plasma display intended for practical use, the plasma display should be excellent in other performances comprehensively as well as the improvement of the luminous efficiency. When the composition and pressure of the discharge gas are changed to improve the luminous efficiency, lifetime may be shortened, and driving may be unstable. Further, for practical use, high definition, high brightness, low cost and so forth are strongly demanded. Thus, it is necessary to take into consideration other conditions (driving conditions, cost, etc.) in addition to the composition and pressure of the discharge gas, in the development of the plasma display of practical use.
The present invention provides a PDP capable of improving luminous efficiency, guaranteeing long lifetime, and being driven stably. Further, the PDP in accordance with the present invention makes possible a high-brightness, high-definition and low-price display device.
To solve the above problems, the features of the present invention include selection of the composition and total pressure of the discharge gas, the pulse width of a write voltage and so forth. Such features contribute to the improved luminous efficiency, guaranteed long lifetime, and elimination of instability in driving.
In the present invention, (1) a discharge-gas mixture containing at least three components of Ne, Xe and He is used, and component proportions of the discharge-gas mixture and a pressure of the discharge-gas mixture and a pulse width for write-discharge are selected as follows.
Conditions for the discharge-gas mixture are as follows:
(2) A Xe proportion is in a range of from 2% to 20%, a He proportion is in a range of from 15% to 50%, wherein (4) the He proportion is greater than the Xe proportion, and (5) a total pressure of the discharge-gas mixture is in a range of from 400 Torr to 550 Torr.
Further, (6) a width of voltage pulses to be applied to address electrodes is 2 xcexcs or less.
Further, the present invention become more practical if it is configured as below.
In a second embodiment of the present invention, a discharge-gas mixture contains a Xe proportion in a range of from 2% to 14% and a He proportion in a range of from 15% to 50% with the He proportion being greater than the Xe proportion; a total pressure of the discharge-gas mixture is in a range of from 400 Torr to 550 Torr; and a width of voltage pulses to be applied to address electrodes is 2 xcexcs or less. The present embodiment is capable of realizing a PDP which is more advantageous in practical use. A sustaining discharge voltage is increased if the Xe proportion is selected to be much greater than 14%.
In a third embodiment of the present invention, a discharge-gas mixture contains a Xe proportion in a range of from 6% to 14% and a He proportion in a range of from 15% to 50% with the He proportion being greater than the Xe proportion; a total pressure of the discharge-gas mixture is in a range of from 400 Torr to 550 Torr; and a width of voltage pulses to be applied to address electrodes is 2 xcexcs or less. This embodiment realizes a PDP which provides particularly high brightness and excellent luminous efficiency.
In a fourth embodiment of the present invention, a discharge-gas mixture contains a Xe proportion in a range of from 6% to 12% and a He proportion in a range of from 15% to 50% with the He proportion being greater than the Xe proportion; a total pressure of the discharge-gas mixture is in a range of from 400 Torr to 550 Torr; and a width of voltage pulses to be applied to address electrodes is 2 xcexcs or less. Advantages achieved by the He proportion is particularly pronounced for the above Xe proportion, and the luminous efficiency is improved effectively to realize a high-brightness PDP.
Needless to say, the PDP of the present invention provides an imaging device capable of the above characteristics.